newpid implements the userland interface to PID namespaces on Linux

It:
- unshare the PID namespace
- unshare the mount namespace (so that it can remount /proc, needed by "ps" and co...)
- start a daemon so that you can further connect to it as many times you wish (like "screen")
- implement pty/tty so that you can run a text editor

CAVEATS:
- there is no protocol besides the initial connection, so once you got a shell inside the instance,
  "window resizes" won't be transmitted to the tty slave
- I didn't bothered to implement a terminal client, so for client-side, newpid forks a "socat" instance
  (which will handle terminal non-canonical mode/raw for us)

==== LAUCH a daemon

newpid --daemon jail
newpid --daemon --chroot=/image/ jail
newpid --daemon --chroot=:/image/ jail

(the ":" in front of the --chroot path here denotes to always chroot no matter if the client used the --chroot flag)

newpid --daemon --nproc=32 jail

==== KILL a daemon

newpid --kill jail

==== RUN something

# open a terminal
newpid jail

newpid jail -- ps auxf
newpid jail -- ls -laF /

# HERE --chroot will make you chroot if the daemon was invoked with --chroot=/path/to/somewhere/
#  if the --chroot path of the daemon was preprended with a ":", you will always be chrooted so the --chroot flag in
# the client is somewhat virtually useless in this case
newpid jail --chroot -- ls -laF /

newpid jail kill -9 -1